A bed with a water-filled mattress can help prevent bed sores (see ULCER – Decubitus ulcer) in patients confined to bed for more than a few days. Its flexibility provides uniform support for the whole body. Air beds are now more often used: they are light and more comfortable and the modern version, called a ripple bed, has a motor that fills and empties tubes in the mattress. The patient's circulation is stimulated and pressure is regularly changed on susceptible parts of the body – elbows, buttocks and heels – thus reducing the likelihood of pressure sores developing, particularly in the elderly.